Modular welding guns

ABSTRACT

An actuator designed for use with a welding gun of the type having a first electrode movable in a straight line toward and away from a second electrode supported by a welding arm. The actuator includes a housing with a first and second end. A bushing with a generally square opening defined therethrough is supported in the first end of the housing. An actuator rod extends through the square opening in the bushing and has a first end inside the housing and a second end disposed external to the housing. The actuator rod has an external surface with a generally square cross section such that the external surface engages the square opening to prevent rotary motion of the rod with respect to the housing. A drive mechanism is disposed in the housing and is operable to move the rod with respect to the housing. The drive mechanism may be a pneumatic actuator or a rotary screw drive.

REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of U.S. patent application Ser. No. 09/641,264, filed Aug. 17, 2000, which claims priority from U.S. provisional patent application Serial No. 60/149,337, filed Aug. 17, 1999, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to spot welding guns and, more specifically, to weld guns that are constructed from modular components.

BACKGROUND OF THE INVENTION

[0003] Traditional spot welding guns are usually custom manufactured for their intended application. These custom weld guns include welding arms that are moved by some type of actuator, such as a pneumatic or servo actuator. The welding arms, yokes, and pivots are often custom configured and may be part of a custom casting including the arms, yokes, pivot supports, and actuator arms. Obviously, custom casting portions of the weld gun raises the cost and complexity of the gun and increases the lead time required for providing the gun for a specific application. In light of this, there is a need for a modular approach to the design and construction of spot welding guns.

SUMMARY OF THE INVENTION

[0004] The present invention improves on the prior art by providing a modular welding gun including a frame and an upper and lower yoke that are both interconnected with the frame. At least one of the yokes is movable with respect to the frame. An upper weld arm has a first end that is removably interconnected with an upper yoke and a second end which is configured to support an electrode. A lower arm has a first end removably interconnected with the lower yoke, and a second end configured to support an electrode. An actuator is operable to move the movably yoke between a welding position and a rest position.

[0005] According to the further aspects of the present invention, an actuator is provided with non-rotate features. The actuator is for use with a welding gun of the type having a first electrode movable in a straight line toward and away from a second electrode supported by a welding arm. The actuator includes a housing with a first and a second end. A bushing with a generally square opening defined therethrough is supported in the first end of the housing. An actuator rod extends through the square opening in the bushing and has a first end disposed inside the housing and a second end disposed external to the housing. The actuator rod has an external surface with a generally square cross section such that the external surface engages the square opening to prevent rotary motion of the rod with respect to the housing. A drive mechanism disposed in the housing is operable to move the rod with respect to the housing. The drive mechanism may be either pneumatic or mechanical.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a perspective view of a first embodiment of a scissors-type modular weld gun according to the present invention;

[0007]FIG. 2 is a perspective view of the weld gun of FIG. 1 showing the opposite side;

[0008]FIG. 3 is yet another perspective view of the weld gun of FIGS. 1 and 2;

[0009]FIG. 4 is a side elevational view of the weld gun of FIGS. 1-3;

[0010]FIG. 5 is a perspective view of a second embodiment of a modular scissors-type servo-actuated welding gun according to the present invention;

[0011]FIG. 6 is a perspective view of the weld gun of FIG. 5 showing the other side;

[0012]FIG. 7 is yet another perspective of the weld gun of FIGS. 5 and 6;

[0013]FIG. 8 is a side elevational view of the welding gun of FIGS. 5-7;

[0014]FIG. 9 is a perspective view of the third embodiment of scissors-type welding gun according to the present invention;

[0015]FIG. 10 is a perspective view of the welding gun of FIG. 9 showing the other side;

[0016]FIG. 11 is yet another perspective of the welding gun of FIGS. 9 and 10;

[0017]FIG. 12 is a side elevations view of the welding gun of FIGS. 9-11;

[0018]FIG. 13 is a perspective view of the fourth embodiment of welding gun according to the present invention;

[0019]FIG. 14 is a perspective view of the welding gun of FIG. 13 showing the other side;

[0020]FIG. 15 is a yet another perspective of the welding gun of FIGS. 13 and 14;

[0021]FIG. 16 is a side elevational view of the welding gun of FIGS. 13-15;

[0022]FIG. 17 is a perspective view of the fifth embodiment of welding gun according to the present invention;

[0023]FIG. 18 is a perspective view of the welding gun of FIG. 17 showing the other side;

[0024]FIG. 19 is a yet another perspective of the welding gun of FIGS. 17 and 18;

[0025]FIG. 20 is a side elevational view of the welding gun of FIGS. 17-19;

[0026]FIG. 21 is a perspective view of the sixth embodiment of welding gun according to the present invention;

[0027]FIG. 22 is a perspective view of the welding gun of FIG. 21 showing the other side;

[0028]FIG. 23 is a yet another perspective of the welding gun of FIGS. 21 and 22;

[0029]FIG. 24 is a side elevational view of the welding gun of FIGS. 21-23;

[0030]FIG. 25 is a perspective view of the seventh embodiment of welding gun according to the present invention;

[0031]FIG. 26 is a cross-sectional view showing the construction of the bearing assembly and the interconnection between the modular weld arms and the upper and lower yokes, taken along lines 26-26 in FIG. 25;

[0032]FIG. 27 is a perspective view of the eighth embodiment of welding gun according to the present invention;

[0033]FIG. 28 is a side elevational view of the welding gun of FIGS. 27;

[0034]FIG. 29 is an additional perspective of the welding gun of FIGS. 27 and 28;

[0035]FIG. 30 is yet another perspective view of the welding gun of FIGS. 27-29;

[0036]FIG. 31 is a perspective view of the ninth embodiment of welding gun according to the present invention;

[0037]FIG. 32 is a side elevational view of the welding gun of FIG. 31;

[0038]FIG. 33 is another perspective view of the welding gun of FIGS. 31 and 32;

[0039]FIG. 34 is yet another perspective view of the welding gun of FIGS. 31-33;

[0040]FIG. 35 is a perspective view of a servo actuator according to a further aspect of the present invention;

[0041]FIG. 36 is an additional perspective view of the servo actuator of FIG. 35 showing the other side;

[0042]FIG. 37 is yet another perspective view of the servo actuator of FIGS. 35 and 36;

[0043]FIG. 38 is a side elevational view of the servo actuator of FIGS. 35-37;

[0044]FIG. 39 is a cross-sectional view of a servo actuator of FIGS. 35-38;

[0045]FIG. 40 is a detailed view of the actuator end of the servo actuator of FIG. 39;

[0046]FIG. 41 is a cross-sectional view of an alternative embodiment of a servo actuator according to the present invention;

[0047]FIG. 42 is an exploded view of the servo actuator of FIG. 41;

[0048]FIG. 43 is a perspective view of another embodiment of a servo actuator according to the present invention;

[0049]FIG. 44 is a side elevational view of the servo actuator of FIG. 43;

[0050]FIG. 45 is another perspective view of the servo actuator of FIGS. 43 and 44;

[0051]FIG. 46 is yet another perspective view of the servo actuator of FIGS. 43-45;

[0052]FIG. 47 is a perspective view of yet another alternative embodiment of a servo actuator according to the present invention;

[0053]FIG. 48 is another perspective view of the servo actuator of FIG. 47;

[0054]FIG. 49 is yet another perspective view of the servo actuator of FIGS. 47 and 48;

[0055]FIG. 50 is a side elevational view of the servo actuator of FIGS. 47-49;

[0056]FIG. 51 is a perspective view of a pneumatic actuator, with non-rotate features, for use with the present invention;

[0057]FIG. 52 is a cross-sectional view of a pneumatic actuator, with non-rotate features, for use with the present invention; and

[0058]FIG. 53 is a perspective view of a bushing for use with the actuators according to the present invention, with a square orifice defined through the bushing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] Referring to FIGS. 1-4, a scissors type modular welding gun according to the present invention is generally shown at 10. This embodiment has an upper weld arm 12 and a lower weld arm 14 which are pivotally interconnected by fulcrum assembly 16. As shown, the fulcrum assembly includes an upper yoke 18, a lower yoke 20 and an isolating bearing assembly 22 that pivotally interconnects the yokes 18 and 20. The upper weld arm 12 clamps to the upper yoke 18 for movement therewith. An actuator arm 24 also clamps to the upper yoke 18 so that the upper weld arm 12, the upper yoke 18, and the actuator arm 24 move as a single unit. In prior approaches to constructing weld guns, the upper yoke 18, upper weld arm 12, and actuator arm 24 would be cast as a single unit requiring a custom casting. In the present invention, the upper yoke is formed from a flat piece of metal with standard bolts interconnecting it with the upper weld arm 12 and the actuator arm 24. The upper weld arm 12 is formed from a piece of copper bar stock, and is clamped to the upper yoke 18. Likewise, the actuator arm 24 is cut from a piece of aluminum stock and bolted to the upper yoke 18.

[0060] Likewise, the lower yoke 20 is bolted to the lower weld arm 14, which is formed from a piece of bar stock. Once again, traditional weld guns include a custom cast lower arm and yoke assembly whereas the present invention allows the use of standardized parts which may be bolted together to form a complete assembly.

[0061] Another difference between the present invention and the prior art is the construction of the bearing assembly 22. In traditional spot welding scissors type guns, the upper and lower yokes surround the bearing from both sides making access to the bearing for servicing difficult. In the present invention, the upper yoke 18 and lower yoke 22 lie side by side and the bearing assembly 22 pivotally interconnects them in a cantilever fashion. As shown, a through bolt 26 passes through the center of the bearing assembly to interconnect the upper yoke 18 and lower yoke 20. This greatly simplifies maintenance since the bearing assembly 20 may be disassembled using readily available wrenches.

[0062] The weld gun of FIGS. 1-4 also includes a main frame 28 which includes an integral robot mount 30 for mounting the weld gun 10 to a robot. The fulcrum assembly mounts to the main frame 28, allowing the upper weld arm 12 to pivot relative thereto. The lower yoke 20 is also mounted to the main frame so that the lower arm does not move relative to the main frame. Alternatively, the lower arm may also pivot relative to the frame. A modular servo actuator 32 also mounts to the main frame 28 and is positioned behind the weld arms 12 and 14. The servo actuator 32 acts to move the actuator arm 24 upwardly and downwardly, thereby pivoting the upper weld arm 12 as required to open and close the electrodes 13 and 15. As shown, the servo actuator 32 has a fulcrum mount 34 allowing it to pivot slightly relative to the main frame 28 as it moves the upper weld arm 12. The main frame 28, including the robot mount 30 and the portion supporting the fulcrum mount 34 of the servo actuator, is all constructed from standardized components which bolt or weld together to form a complete assembly. Again, this is simpler than the prior art approach in which the main frame may be cast or fabricated to include the various mounting surfaces necessary. Also shown in FIGS. 1-4 is a transformer 36 which also mounts to the main frame 28. As will be clear to those of skill in the art, the transformer 36 may also be remotely mounted, depending on the application.

[0063] Obviously, in order to weld using the welding gun of FIGS. 1-4, electrical current must be conducted to or from the electrodes 13 and 15. As best show in FIG. 2, a flexible shunt 40 interconnects the upper weld arm 12 with the transformer 36. A modular shunt clamp 42 bolts to the upper weld arm adjacent the upper yoke 18 and interconnects with the flexible shunt 40. As will be clear to those of skill in the art, the shunt clamp 42 may be clamped to the upper weld arm 12 at various positions along its length, depending on the application. Because the lower weld arm 14 is stationary in this embodiment, a non-flexible shunt 44 extends between the transformer 36 and a second modular shunt clamp 46 which bolts to the lower weld arm 14 adjacent the lower yoke 20. In this embodiment, the modular weld arms 12 and 14 are shown as bar stock having a circular cross-section that has “squared-off” where they bolt to the shunt clamps 42 and 46 in the upper and lower yokes 18 and 20. Alternatively, the weld arms 12 and 14 may have a squared-off cross-section throughout their length.

[0064] Referring now to FIGS. 5-8, a second embodiment of a modular scissors type, servo actuated, welding gun is generally shown at 50. This embodiment differs from the previous embodiment in that the yokes 52 and 54 are taller and the weld arms 56 and 58 are longer. This weld gun 50 is adapted for a different application which requires a wider spacing in between the upper and lower arms 56 and 58 and a greater reach between the yokes 52 and 54 and the electrodes 60 and 62. By comparing the first embodiment and the second embodiment, it can be seen that many of the components are the same or similar. That is, each are formed from modular components which may be interchanged in order to change the configuration of the overall assemblies. In the second embodiment, taller yokes 52 and 54 are used and longer pieces of bar stock are used to form the arms 56 and 58. The bearing assembly 64 is similar and the actuator arm 66 is longer. As will be clear to those of skill in the art, components from the first embodiment and second embodiment may be interchanged so as to form other configurations of weld guns. Also, a variety of actuators may be bolted in place of the servo actuators illustrated so that the weld guns may work with other systems. Another difference between the second weld gun 50 and the first weld gun 10, is that the second weld gun 50 is designed to use a remote transformer, not shown, instead of one mounted to the gun. The necessary shunts for interconnecting with the transformer are not illustrated in these Figures.

[0065] Referring now to FIGS. 9-12, a third embodiment of a weld gun according to the present invention is generally shown at 70. This embodiment is similar to the previous embodiments in that it is constructed from modular components to make a complete working assembly. However, it differs in that it includes a pneumatic actuator rather than a servo actuator. Therefore, both an upper actuator arm 72 and a lower actuator arm 74 extend rearwardly from the fulcrum assembly 76 that pivotally interconnects the upper weld arm 78 and the lower weld arm 80. A pneumatic cylinder 82 is disposed between the ends of the upper and lower actuator arms 72 and 74 so that when the cylinder 82 is actuated and extended, as shown, the actuator arms 72 and 74 are spread apart causing the welding arms 70 and 80 to be pushed together. Once again, as will be clear to those of skill in the art, many of the same components are used to construct this gun as in the previous embodiments. Because this gun 70 includes a pneumatic actuator, it also includes a positioning cylinder 84 which mounts between the frame 86 and an extension to the upper actuator arm 72. The positioning cylinder 84 is used to position the upper weld arm 78 relative to the frame 86 so that a robot, to which the gun 70 is mounted, may position the upper welding arm in a known position. Otherwise, the robot is unable to determine the exact positions of the upper and lower electrodes relative to the frame. This embodiment also is designed for use with a remote transformer and includes a robot mount 88 for mounting the gun to a robot.

[0066] Referring now to FIGS. 13-16, a fourth embodiment of a weld gun according to the present invention is generally shown at 90. This embodiment is similar to the third embodiment except that it is adapted to be a portable weld gun. For this reason, it includes a support member 92 so that the weld gun 90 may be hung from a welder support. It also includes handles 94 and 96 with controls 98 so that an operator may manually control the weld gun. Also, because the gun is designed for portable use, it does not have a positioning cylinder. Once again, the gun 90 is constructed from a variety of modular components to create a complete operating assembly.

[0067] Referring now to FIGS. 17-20, a fifth embodiment of a modular weld gun according to the present invention is generally shown at 100. This gun 100 is a further example of a weld gun constructed from modular components. In this embodiment, smaller and shorter weld arms are used and the yokes are more compact. This embodiment includes a pneumatic actuator and a positioning cylinder and an integral transformer.

[0068] Referring now to FIGS. 21-24, a sixth embodiment of a modular weld gun according to the present invention is generally shown at 102. Like the earlier embodiments, this embodiment is formed from a variety of modular components. Unlike the earlier embodiments, the upper weld arm 104 is bent so as to suit a different application. Also, this gun is configured such that the lower weld arm 106 is the arm which moves rather than the upper arm 104. This embodiment again illustrates the benefits of the present invention which are realized by the combination of modular components. To provide the different configuration, similar components are assembled in a different manner. Also, the bar stock upper arm 104 provides the benefit that the arm may be bent to the configuration necessary. If later a straight upper arm is desired, the bent upper arm 104 may be unbolted and replaced with a different configuration. This is a benefit to all the configurations in that components may be unbolted for replacement as necessary to maintain or reconfigure the gun.

[0069] Referring now to FIGS. 25 and 26, a seventh embodiment of a modular welding gun according to the present invention is generally shown at 110. The welding gun 110 is a scissors-type arrangement having an upper welding arm 112 and a lower welding arm 114 pivotally interconnected by fulcrum assembly 111. The fulcrum assembly includes an upper yoke 113 and a lower yoke 115 and an isolating bearing assembly 116. The entire assembly is supported by a hanger 117 which interconnects with the bearing assembly 116. FIG. 26 is a cross-sectional view showing the construction of the bearing assembly 116 and the upper yoke 113 and lower yoke 115, as well as the interconnection between the yokes and the weld arms. In this embodiment, the weld arms 112 and 114 have generally rectangular cross-sections throughout their length. Alternatively, they may be circular throughout part or all of their length. As shown, the upper yoke 113 includes a front plate 107 and a rear plate 108 which are interconnected by bolts 109. The upper weld arm 112 is clamped between the front and rear plates and preferably nests in recesses defined in the plates. The front plate 107 includes a downwardly extending pivot flange 117 which forms part of the bearing assembly 116. The lower yoke 115 is constructed similarly. Specifically, it has a rear plate 118 and a front plate 119, both with recesses in which the lower weld arm 114 nests. The rear plate 118 has an upwardly extending pivot flange 120 which lays adjacent to the pivot flange 117 of the upper yoke 113. As will be clear to those of skill in the art, the pivot flanges are electrically isolated from one another. However, it can also be seen that they are relatively cantilever to each other to allow for easy disassembly of the bearing assembly 116.

[0070] Referring now to FIGS. 27-30, an eighth embodiment of a modular welding gun according to the present invention is generally shown at 122. This type of welding gun is generally referred to in the industry as a “C” or straight action welding gun. It has a lower C-shaped arm 123 that holds an electrode 124. The second electrode 126, is supported by an actuator 128. The actuator 128 moves the second electrode 126 with a “straight action” towards the first electrode 124. This operation is similar to the way in which a C clamp closes by moving one clamping element directly towards an opposite clamping element. The actuator in the illustrated embodiment is a servo, such as with an internal ball screw arrangement, with an external anti-rotate rod 130. However, as will be discussed later, other types of actuators may be used in place of the illustrated actuator.

[0071] As with the prior embodiments, the gun 122 is made of modular components with the lower C-shaped weld arm 123 made of bar stock. The gun 122 is designed to be supported by a robot and has a robot mount 132. It is also designed for use with a remotely mounted transformer. Obviously, the modular construction of a straight action welding gun differs from the scissors-type gun discussed earlier. However, similar weld arms such as lower weld arm 123 may be used with either embodiment. In addition, the remainder of the straight action welding gun 122 is bolted together as with the prior embodiment. Specifically, a lower yoke 134 bolts to the lower arm 123 and also interconnects with the frame 136 which supports the actuator 128. As with previous embodiments, the yoke 134 comprises a pair of plates which clamp together with the weld arm 123 trapped therebetween. In this way, the lower arm may be easily unclamped from the yoke 134 and replaced or modified.

[0072] Referring now to FIGS. 31-34, a ninth embodiment of a modular weld gun according to the present invention is generally shown at 140. This weld gun 140 is a portable “C” or straight action, pneumatically operated weld gun. Once again, it is assembled from a variety of modular components but differs from the previous embodiment in that it includes a hanger 142 for supporting the portable gun and a pneumatic actuator 144 for moving the electrodes together.

[0073] Referring now to FIGS. 35-38, the design of a servo actuator, which represents a further aspect of the present invention, will be discussed. The servo actuator is generally shown at 150. The servo actuator includes the actuator itself 152 and a drive motor 154. The actuator 152 is designed to work with a variety of motors 154 so the illustrated motor is for illustration purposes only. In fact, the actuator 152 includes an adaptor plate 156 that allows the actuator to mount to any of a variety of servo motors. The actuator includes a central cylindrical portion which contains the ball screw actuator. The cylindrical portion 158 is sandwiched between a front housing 160 and a rear housing 162 that are interconnected by tie rods 164. The tie rods 164 act to clamp the actuator together and allow for easy disassembly. The illustrated front housing 160 has trunnion mounts 166 extending from the sides thereof allowing the actuator to be mounted in a trunnion as part of a scissors type weld gun. The front housing 160 may be interchanged with a different front housing that allows a different mounting arrangement. For example, a front housing with mounting holes therein may be provided so that the actuator can be used as part of a straight action gun.

[0074] Referring now to FIGS. 39 and 40, the internal workings of the actuator of FIGS. 35-38 will be described in more detail. As shown, the motor 154 turns a drive pulley 168 which in turn rotates a driven pulley 170 via a belt 172. The driven pulley 170 drives a screw 174 which extends through the center of the actuator 152. A nut 176 is supported around the screw 174 and moves forwardly and backwardly as the screw 174 turns. Though not shown, the screw 174 and nut 176 form a ball screw arrangement wherein balls ride in grooves cut into the screw and nut. A square rod 178 mates with the forwardmost end of the nut 176 so that it moves forwardly and backwardly with it. In FIG. 37, the front end of the nut 176 and the rear end of the square rod 178 are shown separated by a short distance for detail. However, in use, the rearward end of the square rod 178 would fit over the front end of the nut 176 so that they move together. Traditional ball screws have problems with the output end of the actuator rotating around the central axis of the ball screw as it moves forwardly and backwardly. As shown earlier in FIGS. 27-30, a ball screw servo actuator may include external anti-rotate features. According to the present invention, the square actuator rod 178 has a square cross-section and passes through a square orifice 180 in the front housing 160. As best shown in FIGS. 40 and 41, the square orifice 180 in the housing 160 is defined by a bearing or bushing 179. This bearing or bushing 179 is supported by the front housing 160 and has a square orifice defined therethrough. As shown, the orifice is elongated in the direction of the rod so as to create a large support surface. In one preferred embodiment, the bearing or bushing 179 has an end-to-end length of three to three and one half inches. In other embodiments, the bushing is also elongated, but may have a length of only two inches or more, or one inch or more. However, the highly elongated bushing, with a length of three to three and one-half inches or more is preferred. In some embodiments, the bushing is aluminum with a Rulon® coating. Rulon® is an oil impregnated plastic. The bushing may be made out of other materials as well.

[0075] Therefore, the actuator rod 178 just moves inwardly and outwardly and does not rotate about the central axis of the ball screw. As will be clear to those of skill in the art, the actuator end 182 of the square rod 178 may have various configurations based on the needs of the weld gun which it is designed to actuate. However, the present configuration of servo actuator 150 allows for interchangeability of parts making it easier to adapt the actuator to a variety of applications. Also, the square actuator rod 178 avoids the need for external anti-rotate features.

[0076] Referring now to FIGS. 41 and 42, an alternative embodiment of a servo-actuator is illustrated. Specifically, FIG. 41 shows a cross-sectional view of a servo-actuator similar to the actuator shown in FIGS. 35-39. The actuator portion 180 is shown in exploded form in FIG. 42 to show the internal construction. This embodiment differs from the previous embodiment in that the nut 182 which engages the screw 184 is bolted to the end of the square rod 186 and is a somewhat different shape and size. It can also be seen that the trunnion 188 which defines the actuator end of the actuator portion 180 includes bolt holes 190 for interconnecting the trunnion 188, and the actuator, to a welding gun. A square bearing or bushing 192 fits into the trunnion 188 and defines the square opening in the front of the actuator that prevents rotation of the square rod 186. As with the previous embodiment, the bushing is elongated with a preferred length of three to three and one half inches or more. However, in other embodiments, the bushing may have a length of two inches or more or one inch or more. The bushing has a construction similar to the previously discussed bushing. In FIG. 41, a different motor 194 is shown driving the actuator 180, although a variety of motors may be used.

[0077] Referring now to FIGS. 43-46, another configuration of a servo actuator 200 is shown. In a previous embodiment of a servo actuator, the trunnion mount was located near the actuator end of the actuator while in the servo actuator 200 in FIGS. 43-46, the trunnion mount 202 is mounted towards the rear. As will be clear to those of skill in the art, the modular system of the present invention may be adapted for use with either type of servo actuator.

[0078] Referring now to FIGS. 47-50, yet another version of a servo actuator 210 is illustrated. In this configuration the servo actuator 210 has a flange 212 for mounting it to a welding gun. The modular approach allows this type of actuator to be used as well.

[0079] Referring to FIGS. 51-52, yet another embodiment of an actuator for use with the present invention will be described. The actuator 220 is a pneumatic or air-actuated cylinder with anti-rotate features similar to the previously discussed actuators. As known to those of skill in the art, pneumatic actuators, in a wide variety of designs. The actuator 220 illustrated in FIGS. 51 and 52 is a sophisticated 4-port actuator design. However, the anti-rotate feature according to the present invention is also applicable to other types of pneumatic actuators. The actuator 220 has an outer housing 222 with a forward end 224. A piston rod 226 extends out of the forward end 224. As illustrated, the piston rod 226 has a generally rectangular or square cross-section which meets with a matching opening in the forward end 224 of the housing 222. The rectangular square opening in the housing may be part of the housing, or a bushing, as illustrated. Another bushing 230 is shown in FIG. 53. As will be clear to those of skill in the art, the specific design of the bushing 228 or 230 depends on the application. In some embodiments, the bushing is aluminum with a Rulon® coating. Rulon® is an oil impregnated plastic. The bushing may be made out of other materials as well. As with the previous embodiments, it is preferred that the bushing be elongated with a Length of 3 to 3½ inches or more. In alternative embodiments, the bushing may have a length of only 1 inch or more, or 2 inches or more. Referring again to FIGS. 51 and 52, it can be seen that the piston rod 26 is not required to be square throughout its length. Instead, the tip 232 may be shaped so as to interconnect with other items. Also, internal to the actuator 220, the piston rod 226 is typically rounded cross-section, as best shown in FIG. 52. The actuator 220 is a 4-port design, including a weld forward port 234, a retract forward port 236, a retract return port 238, and a weld return port 240. Internally, the actuator 220 includes a first piston 242 connected to the piston rod near its rear end and a second piston 244 connected to the piston 226 intermediate its two ends. The first piston 242 moves inside an inner cylinder 246, which is movable inside of the housing 222. A separator 248 divides the housing 222 into two sections. In operation, compressed air is introduced into the retract forward port 236, which causes the inner cylinder 246 to move forward until it is stopped by the separator 248. The first piston 242 and second piston 244, along with a piston rod 226, move forwardly with the inner cylinder 246. When compressed air is introduced into the weld port 234, pressurized air is introduced behind the first piston 242 and second piston 244 causing them both to move forwardly, along with the piston rod 226. When compressed air is introduced into the retract return port 238, the inner cylinder 246 is moved rearwardly until stopped by the rear cap 250. The first piston 242, second piston 244, and piston rod 226 move backwardly with the inner cylinder 246. When compressed air is introduced into the weld return port 240, pressurized air is introduced forward of the first and second pistons, causing the pistons 242 and 244 to move rearwardly, along with the piston rod 226.

[0080] As will be clear to those of skill in the art, the present invention may be adapted and modified in various ways without departing from the intent or scope of the present invention. It is the following claims, including all equivalents, which define the scope of the present invention. 

I claim:
 1. A servo actuator for use with a welding gun of the type having a first electrode movable in a straight line toward and away from a second electrode supported by a welding arm, the actuator comprising: a housing having a first and a second end, said first end having a generally square opening defined therethrough; a rotary screw supported in said housing along a longitudinal axis thereof; a drive nut engaged with said screw such that relative rotary motion between said screw and said nut causes said nut to move linearly with respect to said screw; and an actuator rod extending through said square opening in said housing and having a first end interconnected with said drive nut and a second end disposed external to said housing, said actuator rod having an external surface with a generally square cross section such that said external surface engages said square opening to prevent rotary motion of said rod with respect to said housing.
 2. A servo actuator according to claim 1, wherein said screw and said nut comprise a ball screw and a ball nut.
 3. A servo actuator according to claim 1, further comprising a motor mounting plate for mounting a drive motor operable to rotate said screw.
 4. A servo actuator according to claim 3, wherein said motor mounting plate includes means for accommodating a variety of motors.
 5. An actuator for use with a welding gun of the type having a first electrode movable in a straight line toward and away from a second electrode supported by a welding arm, the actuator comprising: a housing having a first and a second end, said first end having a bushing with a generally rectangular opening defined therethrough; an actuator rod extending through said square opening in said bushing and having a first end disposed inside said housing and a second end disposed external to said housing, said actuator rod having an external surface with a generally rectangular cross section such that said external surface engages said generally rectangular opening to prevent rotary motion of said rod with respect to said housing; and a drive mechanism disposed in said housing operable to move said rod with respect to said housing.
 6. The actuator according to claim 5, wherein the generally rectangular opening in the bushing is generally square, and the external surface of the actuator rod has a generally square cross section.
 7. The actuator according to claim 5, wherein the drive mechanism comprises a pneumatic drive unit.
 8. The actuator according to claim 5, wherein the drive mechanism comprises a rotary screw driving a drive nut.
 9. The actuator according to claim 5, wherein the generally rectangular opening in the bushing comprises an elongated passage with a generally rectangular cross section, the passage having a length greater than 1 inch.
 10. The actuator according to claim 5, wherein generally rectangular opening in the bushing comprises an elongated passage with a generally rectangular cross section, the passage having a length greater than 3 inches.
 11. An actuator for use with a welding gun of the type having a first electrode movable in a straight line toward and away from a second electrode supported by a welding arm, the actuator comprising: a housing having a first and a second end, said first end having a bushing with a generally square opening defined therethrough; an actuator rod extending through said square opening in said bushing and having a first end disposed inside said housing and a second end disposed external to said housing, said actuator rod having an external surface with a generally square cross section such that said external surface engages said square opening to prevent rotary motion of said rod with respect to said housing; and a drive mechanism disposed in said housing operable to move said rod with respect to said housing. 